It is well known in the Gallium Arsenide (GaAs) industry that a etch pit density (EPD) level of a substrate is very important in minority carrier device reliability and in the yield of devices from the substrate. However, in GaAs electronic devices, such as hetero-structure bipolar transistors (HBTs) and pseudomorphic high electron mobility transistors (pHEMTs), substrate EPD is not known to be a determining factor in device yield.
Wafer annealing is well known. In addition, ingot annealing is known as described in “Improved Uniformity of LEC Undoped Gallium Arsenide Produced by High Temperature Annealing” by Rumsby et al., GaAs IC Symposium, pp. 34-37 (1983).
Techniques for growing semiconductor crystals using a vertical gradient freeze (VGF) and carbon doping are known, such as those disclosed in U.S. Pat. No. 6,896,729 to Liu et al VGF fabrication consistent with the innovations here encompass crystal growth technology, apparatus, and processes whereby large single crystal ingots are grown with a very high level of structural uniformity and low defect density. According to one exemplary implementation, controlled growth of GaAs is achieved by placing a dopant material in an ampoule outside a growth crucible, not in contact with the molten charge. Since the dopant materials are separated from the melt or the internal wall of the crucible, the process is favorable for achieving a high single crystal growth yield. An exemplary VGF process for achieving controlled incorporation of carbon in the growth of semi-insulating GaAs material, is as follows: (1) loading charges of GaAs raw materials into the crucible, (2) placing carbon doping sources within, generally at a low end of, the ampoule, (3) loading the crucible with the GaAs charges into the ampoule, (4) evacuating/sealing under vacuum the ampoule containing the dopant, the crucible, the GaAs charges, and B2O3 material, and (5) heating/melting the charge and then controlling the liquid-solid interface, wherein control of the amount of the dopant and/or the temperature are used to grow semi-insulating GaAs ingots with high uniformity and low defects. It is desirable to provide a method for manufacturing low etch pit density (EPD) InGaP and GaAs wafers using annealing and VGF and it is to this end that the present invention is directed.